The present invention relates to an apparatus for controlling a reduction ratio in a continuously variable transmission.
U.S. patent application Ser. No. 486,448 filed Apr. 19, 1983, now U.S. Pat. No. 4,597,308, discloses an apparatus for controlling a reduction ratio of a continuously variable transmission. According to this known apparatus, a shift reference switch is turned on when the continuously variable transmission has attained the largest reduction ratio, a shift actuator in the form of a stepper motor is actuated in an open loop manner to achieve a desired reduction ratio, a parameter (this parameter being called a "pulse number NA" in this U.S. patent) is stored which is indicative of the position of the shift actuator, and, the parameter is reset to a predetermined value whenever the shift reference switch is turned on. This known apparatus does not require the detection of an actual reduction ratio or an actual shift actuator operating position because of the shift reference switch. Since according to this known apparatus the shift actuator is caused to move to a predetermined position which causes the continuously variable transmission to attain the largest reduction ratio whenever the ignition switch is turned on or a computer of the apparatus is reset, the shift actuator will move toward the predetermined position to shift the transmission toward the largest reduction ratio if the ignition switch is turned on after having been turned off unintentionally during running of the motor vehicle or the computer is reset during running of the motor vehicle owing to generation of noise. If the shift motor should move to the predetermined position during running of the vehicle, the transmission shifts toward the largest reduction ratio, subjecting the vehicle to rapid engine braking to the extent that the engine may overrun.
An object of the present invention is to improve an apparatus for controlling a continuously variable transmission of the above mentioned type such that the above mentioned problem will not arise even if an ignition switch is turned on after the ignition switch has been turned off unintentionally during running of the motor vehicle or the computer of the apparatus has been reset during running of the motor vehicle.